There has been known an image forming apparatuses of a type that is provided with a plurality of cartridges accommodating toner therein. The cartridges can be attached to, and detached from, the image forming apparatus.
Prior art discloses an image forming apparatus that includes a drum unit and a plurality of developer cartridges. The drum unit can hold a plurality of developer cartridges. The drum unit is movable between an inside position, at which the drum unit is disposed inside of the casing of the image forming apparatus, and an outside position, at which the drum unit is disposed outside of the casing of the image forming apparatus.
Each developer cartridge includes a detecting gear. The detecting gear includes a protrusion. The drum unit includes a lever. The main body casing includes a photo-sensor. After the developer cartridge is attached to the drum unit, when the detection gear rotates, the protrusion abuts on the lever, whereupon the lever pivotally moves. The photo-sensor detects the pivotal movement of the lever, and generates a signal. Based on the signal outputted from the photo-sensor, the image forming apparatus acquires the information on the developer cartridge.